Heavy oil from oil sands may be recovered using a thermal in-situ recovery process, such as: steam-assisted gravity drainage (SAGD), expanding solvent steam-assisted gravity drainage (ES-SAGD), cyclic steam stimulation (CSS), steamflooding, solvent-assisted cyclic steam stimulation, toe-to-heel air injection (THAI), or a solvent aided process (SAP).
Gas produced from oil sands recovery processes often contains sulfur in the form of H2S and organosulfur compounds, as well as CO2, naphthenes, and aromatics. It is desirable to remove at least a portion of the sulfur, for example, in order to meet regulatory requirements for reducing emissions.
The selection of suitable sulfur removal processes for gases produced during oil sands production of heavy oil is challenging due to the complex nature of the organosulfur species present in the heavy oil. Organosulfur compounds are compounds that include a thiol (—SH) chemical functionality. These compounds are also known as mercaptans. Examples of organosulfur compounds that are found in gases produced during oil sands production of heavy oil include: methylmercaptan, ethylmercaptan, and propylmercaptan.
Specific process conditions may reduce the effectiveness of a sulfur removal process. Amine/Claus technology is the conventional technology selection for sulfur inlet gas rates above 10 to 20 tonnes/day. Claus Plant performance requires a minimum H2S concentration to sustain combustion in the reaction furnace. Oil sands produced gas often has high ratios of CO2:H2S which may preclude the use of this technology.
Non-regenerable scavengers of H2S have been used with mixed success. However, the operating costs are prohibitive and significant solid or liquid waste is generated. These processes are typically not attractive at sulfur removal rates above 100-200 kg/day for typical plant sizes.
A liquid reduction-oxidation (redox) process is typically used for sulfur removal in the range of 100 kg/day to 10 tonne/day; however, the contaminants in oil sands produced gases pose some challenges for liquid redox processes. Organosulfur compounds absorbed from the gas by a lean liquid redox solution may exit the system in the oxidizer vent, creating unwanted emissions, or be converted into disulfides (RS-SR compounds) that exit the system with the sulfur product. The formation of disulfides has the potential to impact liquid redox solution performance and pose undesirable odor and exposure issues when the sulfur product is handled.
U.S. Pat. No. 7,674,444 to Mak discloses a process in which H2S and other sulfur species are absorbed in a lean hydrocarbon liquid. The sulfur species are subjected to catalytic conversion into disulfides, which are removed from the hydrocarbon liquid. The sulfur free hydrocarbon liquid is regenerated in a distillation column and/or refinery unit, and light components are recycled to the absorber. Selective separation of H2S and mercaptan components via distillation can be difficult, distillation columns can be expensive to build, and/or distillation columns can require large amounts of energy to operate.